This application is a continuation-in-part application of application Ser. No. 458,784, filed Dec. 29, 1989.
The present invention relates to a method and apparatus for producing a water/abrasive mixture for cutting and cleaning surfaces or objects and for the precise removal of material, by introducing an abrasive, in a mixing chamber, into a jet of water that is under high pressure and that passes through the mixing chamber from an inlet to an outlet thereof.
Methods of this general type are known where particles of hard material (abrasive) are added to high pressure water jets to produce a mixture for cleaning and cutting surfaces or objects. The advantage of using such water/abrasive mixtures rather than utilizing a thermal process for cutting objects is that the cutting location remains practically cold, which is of particular advantage when using the process for cutting or cleaning objects that are sensitive to heat. Water/abrasive mixtures are also very suitable for cutting and cleaning or for the removal of material in underwater applications.
With one known method of the aforementioned general type (U.S. Pat. No. 4,648,215, Hashish et al, issued Mar. 10, 1987), abrasive is added to a water jet that passes through a mixing chamber of an apparatus for cutting and cleaning via a water/abrasive mixture. In particular, the abrasive is supplied at an acute angle relative to the water jet. The diameter of the mixing chamber is less than the free length of the jet in the chamber.
This known supply technique results in the considerable drawback that after a short period of use, pits or cavities form in the wall of the mixing chamber on that side opposite the abrasive nozzle; these cavities rapidly become very large. As a result of the formation of these disadvantageous cavities, the known apparatus, already after a relatively short period of use, can no longer operate as designed.
Pursuant to the known apparatus of the aforementioned U.S. Pat. No. 4,648,215, an attempt was made to check this phenomenon by providing at least that lower portion of the mixing chamber where the outlet is provided with a hard metal lining that on the one hand has the drawback that it considerably increases the cost of producing such an apparatus, and on the other hand also leads to erosion effects in the abrasive introduction nozzle that is directed into the mixing chamber due to the fact that the lining scatters abrasive back. This caused considerable wear of the nozzle, so that tests under actual conditions of use showed that this known apparatus, and the method carried out therewith, fell short of expectations.
It is therefore an object of the present invention to provide a method and apparatus for improving the effectiveness of the mixing process in the mixing chamber, of increasing the output (hydraulic capacity), and increasing the service life of the mixing chamber and of the discharge nozzle.